Articulated rabbit systems are known for moving the measurement apparatus, which apparatus may either be incorporated in the rabbit itself, or else it may be towed behind the rabbit like a trailer. By way of example, mention may be made of French patent application 2,689,210 published on Oct. 1, 1993, which describes one such articulated drive rabbit, and which recalls the state of the art in this field and the problems posed by such systems: that document teaches "an articulated rabbit for modifying, maintaining, and inspecting pipework, in particular pipework for transporting oil products, the rabbit being of the type comprising at least two identical tubular bodies or `trailers` disposed in alignment with each other and each provided on its outside wall with flexible and strong annular cups having an outside diameter that is substantially equal to the inside diameter of the pipework, and such that at least two trailers are in simple contact via their adjacent ends and are mechanically connected together by means of a flexible resilient coupling element such as a cable or a spring that passes axially through the chambers inside the two trailers and that exerts opposing traction forces on the trailers tending to press their adjacent ends against each other".
Such a system is indeed capable of passing through junction zones in the pipework while maintaining contact between at least one cup and the wall of the pipework so as to ensure continuity of propulsion, and it is also capable of negotiating bends without requiring a ball-and-socket or a universal joint and connection rod system for articulation purposes as exists elsewhere, which systems are either too fragile or else so heavy as to increase the wear of the supporting cups. Nevertheless, the need to have two tubular bodies each having at least two annular cups situated a certain distance apart does not enable such a rabbit to negotiate 90.degree. sharp bends having a small radius of curvature, e.g. 1.5 times the diameter of the pipework, without running the risk of jamming, yet such bends often exist in pipe networks, particularly when the pipes are of small diameter. Indeed, small-diameter pipework prevents the use of ball-and-socket or universal joint type articulation systems which are then incapable, as indeed is the linking system of the above-mentioned patent application, of accommodating offsets between the axes of the articulated elements relative to the axis of the pipework without crushing and deforming the cups, thereby giving rise to the risks of the device becoming mechanically jammed in a bend, or else of the cups no longer providing sealing, which will in any case cause the device to stop moving.